1. Field of the Invention
This invention relates to a method of controlling the flow of combined exhaust gases containing SO.sub.2 from a smelting furnace and a converter furnace to a sulfuric acid plant, the smelting furnace being in continuous operation and the converter furnace in intermittent operation, and more particularly to a method of minimizing the gas pressure fluctuations as the gases pass into the sulfuric acid plant.
2. Description of the Prior Art
In the smelting of copper or nickel, there is usually employed a smelting furnace, e.g., a blast furnace, a reverberatory furnace or a flash smelting furnace, for the melting of the input ores to produce a matte rich in copper or nickel. As the ores, flux and fuel are continuously fed to the smelting furnace, and as air or oxygen-enriched air containing the required amount of oxygen is continuously supplied so as to smelt the ores, a substantially constant amount of exhaust gases containing SO.sub.2 will be generated. The amounts of these exhaust gases produced during operation will fluctuate very little, unless some external factor comes into play.
On the other hand, in a converter furnace operation for copper or nickel, as the steps of the matte charging, slag formation, and blister copper or finished matte product discharging are repeated, air will be frequently supplied to the converter furnace and then stopped. Accordingly, the generation of exhaust gases containing SO.sub.2 will be repeatedly started and stopped, and, in the case of a copper converter furnace, the amount of exhaust gases generated per unit time will substantially correspond to the amount of exhaust gases generated in the smelting furnace.
The total amount of exhaust gases generated in such smelting and converter furnaces must be led to and treated in a sulfuric acid plant. However, if the amount of suction gases is too little, gas will leak out of the treatment apparatus to cause a pollution, whereas if the suction amount is excessive, gas leakage will not be occurred, but excess free air will be sucked in to unnecessarily dilute the SO.sub.2 -containing gases, and not only will excess power be required but also the operation of the sulfuric acid plant will detrimentally affected.
Particularly in the situation wherein the operation of the converter furnace is intermittent, at the point in time when the operation is started and stopped, the gas pressure within the system will sudddenly fluctuate very drastically due to the large variation in the amount of exhaust gases emitted therefrom. Therefore, as a conventional operating method, a procedure is followed wherein as the amount of exhaust gases fluctuates greatly, the rotational speed of the main blower of the sulfuric acid plant will be elevated or lowered by a manual operation in advance and the damper opening in the blower will be manually adjusted so as to compensate in advance for the coming fluctuation. In another method, as described in Japanese Patent Publication No. 9164/77 Published on Mar. 14, 1977, entitled "Method of Controlling Gas Pressures in Copper Converter Furnace Steps," the fluctuation in the gas amounts of exhaust gases being led to the sulfuric acid plant is compensated for by changing the set pressure valve as the pressure suddenly fluctuates, while automatically controlling the gas pressure. However, with the adjustment of the rotation speed of the main blower in the first method, the response time is so delayed that, in the case of a sudden fluctuation in the gas pressure, too much time is required to compensate for the fluctuation, and at the same time with the adjustment of the opening of the damper at the inlet of the main blower by manual action, a fine adjustment will be difficult to make and the temporary leakage of gas or the suction of excess air cannot be prevented. Even when the second-mentioned method is used, a larger pressure fluctuation will occur in the entire system. Thus, the prior art methods have undesirable defects which affect the stability of the operation of each furnace, as well as the operation of the sulfuric acid plant.